This invention relates in general to covered hopper cars and more particularly to hold down bars for securing covers that close the hatches on such cars.
Some granular and nodular materials as diversified as grains and cement should not be exposed to moisture, yet because they are commodities, they must be shipped at the least possible expense. The covered hopper cars used on American railroads serve this purpose. This type of car has side and end walls as well as a bottom wall provided with discharge openings which are normally closed by hinged doors. In addition it has a slightly arched roof which is provided with a hatch in the form of an elongated opening that extends substantially the entire length of the roof and walkways located along both sides of the hatch. Several hatch covers, which are hinged to the roof along one side of the hatch, normally cover the hatch, these covers being located in succession along the hatch so that each extends over a portion of the hatch.
The hatch covers carry gaskets which seat against the upper edge of the wall that encloses the hatch so as to exclude contaminants, most notably water, at this location. While gaps exist between the hatch covers themselves, these gaps are closed with so-called hold down bars, which like the hatch covers, are hinged to the roof along one side of the hatch. The bars extend over the closed hatch covers at the gaps and are engaged by latching devices on the other side of the hatch. Additional hold down bars extend over the ends of the hatch covers at the two ends of the hatch. The bars likewise carry gaskets, and these gaskets seat against the hatch covers to each side of every gap so as to prevent contaminants from seeping into the gaps. Just as significantly, the bars hold the hatch covers down and indeed compress the gaskets on the undersides of the covers against the upper margin of the hatch.
Although hatch covers are fabricated from a lightweight material, such as fiberglass or aluminum, they can vary from 8 to 13 feet in length and can weigh in excess of 100 lbs., making them somewhat difficult to open. Moreover, those charged with loading hopper cars do not handle such covers gently. Typically these workmen unlatch the hold down bars, lift them upwardly and then swing them backwardly until they impinge against the car roof or the walkway near their hinge joints. Ordinarily the hold down bars can withstand this abuse. However, the workmen treat the hatch covers similarly, and they fall backwardly against the hold down bars, causing the bars to bend backwardly still farther under the substantial weight of the hatch covers. Indeed, the force of the impacts from the covers is often enough to deform and damage the hinge brackets for the hold down bars and hatch covers, not to speak of the bars themselves and the walkways against which they bear.
Aside from the foregoing, a steel hold down bar in common use has its gasket bonded to it with an adhesive, but the steel of the bar in time rusts which causes the adhesive bond between it and the gasket to deteriorate. If the gasket breaks loose, the sharp edges of the steel cut into the upturned edges on the two hatch covers over which the bar normally extends and damage the ends of those covers, making it necessary to replace the damaged covers and the gasket to again have a serviceable rail car.
Indeed, replacing a gasket on a hold down bar of conventional construction is not a simple matter, for usually the entire bar must be removed and taken to a shop where its gasket is removed and a new one installed in its place. This can be a difficult and costly procedure. Stripping a defective gasket and applying a new one in the field, that is without removing the hold down bar, is even more difficult and costly.
Furthermore, conventional hold down bars are designed to accommodate rail cars of only one design. Thus, a railroad must maintain an inventory of complete bars varied enough to service cars of several designs.